Yeast fermentation of starch and sugar containing agriculture products such as sugar cane, corn, wheat, barley and sugar beet commonly produces a final solution of ethanol in water and other organic and inorganic compounds called beer. In the fuel ethanol industry and other distilleries, the beer is passed to a distillation column where the ethanol is evaporated leaving a complex aqueous solution of materials that includes ions, organic compounds and other compounds. This material is called stillage. A solid-free clear solution arising from stillage is called thin stillage, which comprises a dilute stream of organic and inorganic compounds. Due to its high biochemical oxygen demand (BOD), it is undesirable to dispose of thin stillage without digestion. In addition, its relatively low value as a nutrient makes it undesirable to concentrate by evaporation.
Thin stillage is usually processed by drying to generate solids called distillers dried grains with solubles (DDGS) that can be used in animal feeds. To make DDGS, thin stillage has to be concentrated into syrup before mixing with wet cake. The process to concentrate thin stillage is not energy efficient as it consumes about 40-45% of the thermal energy required to evaporate and dry thin stillage, and 30-40% of the electrical energy utilized in a dry-grind facility. Accordingly, the energy required to evaporate the large amount of water entrained in thin stillage is a major cost in the ethanol industry. Peyton et al., 2007 (U.S. Pat. No. 7,267,774) teaches an efficient process whereby discharged still bottoms may be filtered in their pasteurized state under sanitary conditions with the water and nutrients directly recovered for beneficial human consumption while the solid concentrate is conveyed to a anaerobic bioreactor that recovers methane to power the pressurized membrane filtration. The need for this process is driven by the significant BOD of the thin stillage making it undesirable to dispose of this stream without digestion and its relatively low value as a nutrient making it undesirable to concentrate by evaporation.
Newkirk et al. (U.S. Pat. No. 7,090,887) disclose a multistage extraction protein extraction and recovery process using water and CaO to adjust pH. Diosady et al. (U.S. Pat. No. 4,889,921) extracted 100 g of rapeseed meal with 1,800 g of water. Murray (U.S. Pat. No. 5,844,086) extracted 50 kg of commercial canola meal with 500 L of water. In all of these extractions the percent of protein concentrate recovered to water used in extraction and processing is less than 3%. Neilsen and Helmer (U.S. Pat. No. 5,989,600) describe using phytase to enhance protein recovery after suspending soy protein concentrate in deionized water at 50° C.